Ankylosing spondylitis is a form of joint inflammation that primarily affects the spine. It can cause the bones of the spine to fuse together over time, a process called ankylosis.
The cause of the disease is unknown. Scientists think a combination of factors, including genetic and environmental, may play a role in its development.
Risk factors of ankylosing spondylitis
There are several risk factors associated with ankylosing spondylitis:
Gender
Men are at higher risk of developing the disease than women.
Age
The condition usually develops in late adolescence or early adulthood.
Genetic makeup
Variations in a number of genes increase the risk of someone developing ankylosing spondylitis.
HLA-B gene
HLA-B produces a protein that plays an important role in the immune system. It is part of the human leukocyte antigen complex, which generates cell-surface proteins that help the immune system differentiate between the body’s own molecules and invaders. HLA-B has a lot of variations, allowing a person’s immune system to react to a wide range of foreign proteins.
A variation of the HLA-B gene called HLA-B27 is thought to increase the risk of developing ankylosing spondylitis, but how this happens is not known. Many people with the condition have the HLA-B27 variation but only a few people with it develop the disorder.
Other genes
Variations in other genes, including ERAP1, IL1A, and IL23R, have also been associated with ankylosing spondylitis. Although they play critical roles in the immune system, it is not clear how these variations affect a person’s risk of developing ankylosing spondylitis.
Researchers believe that changes in genes that have yet to be identified also may affect the risk of a person developing ankylosing spondylitis and influence its progression.
Inheritance
Ankylosing spondylitis is not purely a genetic disease, although it can occur in more than one person in a family. Since the risk of developing the disorder is likely influenced by multiple genetic and environmental factors, if someone inherits a genetic variation linked to ankylosing spondylitis, this does not mean they will develop it. This is true even when more than one family member has the disorder.
The risk of a child developing ankylosing spondylitis is less than 20 percent if their parents carry the HLA-B27 gene. This means that about 80 percent of children who inherit HLA-B27 from a parent with ankylosing spondylitis do not develop the disorder. A person is three times more likely to develop the disease if they have a close relative with the condition.
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